Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of thrombin on the release of tissue plasminogen activator from endothelial cells was studied in primary cultures of human umbilical vein endothelial cells. Tissue plasminogen activator concentration in conditioned medium was measured by a two-site radioimmunometric assay. The addition of increasing concentrations (0.01 to 10 U/ml) of thrombin to confluent cultures produced a saturable, dose-dependent increase in the rate of release of tissue plasminogen activator. A sixfold increase in tissue plasminogen activator concentration (from 2 to 12 ng/ml) occurred after the addition of 1 U/ml thrombin (8 X 10(-9) M) to cultures containing 5 X 10(4) cells/cm2. Enhanced release was not observed until 6 h after thrombin addition, reached a maximum rate of 1.3 ng/ml per h between 8 and 16 h, and then declined to 0.52 ng/ml per h after 16 h. The 6-h lag period before increased tPA release was reproducible and independent of thrombin concentration. Thrombin inactivated with diisopropylfluorophosphate or hirudin did not induce an increase in tissue plasminogen activator levels. A 50-fold excess of diisopropylfluorophosphate-treated thrombin, which inhibits binding of active thrombin to endothelial cell high affinity binding sites, did not inhibit the thrombin-induced increase. It is concluded that proteolitically active thrombin causes an increase in the rate of release of tissue plasminogen activator from cultured human endothelial cells. The 6-h interval between thrombin treatment and enhanced tissue plasminogen activator release may reflect a delaying mechanism that transiently protects hemostatic plugs from the sudden increase in the local concentration of this fibrinolytic enzyme.
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PMID:Thrombin stimulates tissue plasminogen activator release from cultured human endothelial cells. 654 70

Tissue plasminogen activator (t-PA) causes fibrinogen proteolysis when alpha 2-antiplasmin levels fall, and this may contribute to t-PA-induced hemorrhage. Because clot-bound plasmin is protected from alpha 2-antiplasmin inhibition, we tested the possibility that alpha 2-antiplasmin supplementation would block t-PA-induced fibrinogenolysis and bleeding without affecting thrombolysis. When added to human or rabbit plasma, alpha 2-antiplasmin inhibits t-PA-induced fibrinogenolysis, but hat little effect on the lysis of 125I-fibrin clots. To examine its effect in vivo, rabbits with preformed 125I-labeled-jugular vein thrombi were randomized to receive t-PA, t-PA and alpha 2-antiplasmin, or saline. alpha 2-Antiplasmin infusion produced a modest decrease in t-PA-induced thrombolysis (from 40.2% to 30.1%, P = 0.12), but reduced fibrinogen consumption from 87% to 27% (P = 0.0001), and decreased blood loss from standardized ear incisions from 5,594 to 656 microliter (P < 0.0001). We hypothesize that alpha 2-antiplasmin limits t-PA-induced hemorrhage by inhibiting fibrinogenolysis and subsequent fragment X formation because (a) SDS-PAGE and immunoblot analysis indicate less fragment X formation in alpha 2-antiplasmin treated animals, and (b) when added to a solution of fibrinogen and plasminogen clotted with thrombin in the presence of t-PA, fragment X shortens the lysis time in a concentration-dependent fashion. These findings suggest that fragment X incorporation into hemostatic plugs contributes to t-PA-induced bleeding. By blocking t-PA-mediated fibrinogenolysis, alpha 2-antiplasmin supplementation may improve the safety of fibrin-specific plasminogen activators.
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PMID:Alpha 2-antiplasmin supplementation inhibits tissue plasminogen activator-induced fibrinogenolysis and bleeding with little effect on thrombolysis. 768 69

We have investigated human neonatal fibroblast synthetic activity in response to fibrin substrates and components of fibrin formation and degradation. Greater than threefold downregulation of procollagen mRNA levels was seen 24 hours after fibroblasts were grown on fibrin gels as compared to tissue culture plastic. This downregulation occurred in both reptilase-generated fibrin (retention of fibrinopeptide B) and thrombin-generated fibrin (loss of both fibrinopeptide A and B). However, fibroblasts grown on fibrin retained their capacity to respond to the stimulatory action of transforming growth factor (TGF)-beta 1. Fibroblasts seeded on reptilase-generated fibrin displayed an abnormal morphology manifested by dendritic appearance and cell rounding, while fibroblast attachment was enhanced by 30% on thrombin-generated fibrin substrate (P < 0.02). Fibrinopeptides A and B, which are generated during fibrin formation, increased and decreased procollagen mRNA levels, respectively. Tissue plasminogen activator (t-PA) increased procollagen mRNA and TGF-beta 1 levels as early as 6 hours after cells were grown on tissue culture plastic, but this stimulation did not occur in cells cultured on a fibrin substrate. We conclude that alpha 1(I) procollagen mRNA levels in cultures of human dermal fibroblasts are consistently down-regulated by a fibrin substrate and are directly and profoundly influenced by complex interactions between components involved in the formation and removal of fibrin.
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PMID:Decreased levels of alpha 1(I) procollagen mRNA in dermal fibroblasts grown on fibrin gels and in response to fibrinopeptide B. 781 54

Tissue plasminogen activator (t-PA) produced by vascular endothelial cells converts plasminogen to plasmin which degrades fibrin. Since t-PA activity is greatly potentiated in the presence of fibrin (1,2), the activator is implicated in intravascular fibrinolysis. On the other hand, endothelial cells also produce plasminogen activator inhibitor-1 (PAI-1) (3). The inhibitor associated with vascular endothelium rapidly inhibits t-PA, while that released into the liquid phase has a little anti-activator activity (4). However, clinical studies have shown that elevation of plasma PAI-1 level is a risk factor of thrombosis (5,6). It is thus suggested that the balance between t-PA and PAI-1 is important for the regulation of fibrinolysis. The release of t-PA and PAI-1 from vascular endothelial cells is regulated by physiological factors including thrombin (3,7), histamine (8), vasoconstrictor peptide endothelins (9,10) and cytokines (11). In addition, the regulation of the t-PA release and that of the PAI-1 release are not necessarily coupled. It has been shown that activated protein kinase C and cyclic AMP are involved in the stimulation and suppression, respectively, of the endothelial t-PA and PAI-1 production (12,13). However, the role of intracellular calcium in the regulation of endothelial t-PA and PAI-1 release has remained to be elucidated. In the present study, we investigated the effect of calcium ionophore A23187 on the release of t-PA antigen (t-PA:Ag) and PAI-1 antigen (PAI-1:Ag) from cultured vascular endothelial cells derived from human umbilical vein.
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PMID:Calcium regulation of tissue plasminogen activator and plasminogen activator inhibitor-1 release from cultured human vascular endothelial cells. 802 17

Endothelial release of tissue plasminogen activator (t-PA) may initiate fibrinolysis. Fibrinolysis and coagulation were investigated in 12 patients undergoing elective coronary artery bypass surgery. Cardiopulmonary bypass (CPB) was 108 +/- 7 min (mean +/- SEM), the time of cold, crystalloid, retrograde cardioplegia 53 +/- 5 min. Arterial and coronary sinus blood were sampled concomitantly before cardioplegia and after release of the aortic cross-clamp, for measurement of t-PA antigen (Ag) and activity, plasminogen activator inhibitor (PAI-1) Ag and activity, t-PA/PAI-1 complex, single chain urokinase (sc-uPA) and urokinase (uPA) plasminogen activators, the fibrin split product D-dimer, thrombin-antithrombin complex (TAT), and the prothrombin split product F 1 + 2. Cardiopulmonary bypass significantly increased t-PA Ag and activity, t-PA/PAI complex, D-dimer, TAT, and F 1 + 2, and decreased PAI-1 Ag and activity in arterial blood; uPA and sc-uPA were unchanged. The tissue plasminogen activator antigen was higher in coronary sinus than arterial blood after 1 (39 +/- 5 vs 24 +/- 4 ng/ml, P < 0.003), 4 (P < 0.003), and 10 min (P < 0.004) reperfusion. Tissue plasminogen activator activity and t-PA/PAI complex increased, PAI-1 activity decreased, while all other parameters were unchanged across the coronary circulation. In conclusion, CPB induces fibrinolysis and coagulation. Cold cardioplegia induces t-PA release in the coronary circulation, denoting a postischemic antithrombotic function of the coronary endothelium. Tissue plasminogen activator may be used to evaluate endothelial stimulation or injury induced by CPB, or by different regimens of myocardial protection.
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PMID:Fibrinolysis during cardiac surgery. Release of tissue plasminogen activator in arterial and coronary sinus blood. 808 78

Abnormalities of blood coagulation and fibrinolysis are a major part of fulminant liver failure. In this study, the key components of the fibrinolytic system were determined in 42 patients with this condition. Admission levels of plasma plasminogen activity were low (9.1% of normal), as to a lesser extent were the activities of its inhibitors alpha 2-antiplasmin (20.5% of normal) and C1 inhibitor (64% of normal). Tissue plasminogen activator activity was found at normal levels, whereas the level of its fast inhibitor, plasminogen activator inhibitor-1, was greatly increased compared with that of controls (24.3 U/ml and 7.4 U/ml, respectively), indicating a shift toward inhibition of fibrinolysis in these patients. Thrombin-antithrombin complex levels in plasma were significantly increased in fulminant liver failure compared with those in controls (33.5 micrograms/L vs. 2.5 micrograms/L, p < 0.001), indicating activation of coagulation in these patients. High plasma levels of D-dimer, a fragment of cross-linked fibrin, were also found (1,510 micrograms/L vs. 33 micrograms/L in controls, p < 0.001); this finding correlated with the increased level of thrombin-antithrombin complex (r = 0.61, p < 0.001), consistent with activation of fibrinolysis resulting from intravascular coagulation. In conclusion, there are gross abnormalities of the fibrinolytic system in fulminant liver failure, but because inhibitory activity appears to be present in adequate quantities, this limits the incidence of bleeding due to fibrinolysis.
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PMID:Activation of the fibrinolytic system in patients with fulminant liver failure. 824 60

Circulating levels of thrombin-antithrombin III complex (TAT) and plasmin-alpha 2 plasmin inhibitor complex (PIC) in 49 septic patients (23 patients with organ dysfunction (OD), 26 without OD) and 11 postgastrectomy patients were measured to determine the significance of the coagulation-fibrinolytic systems in the development of OD. Tissue plasminogen activator (t-PA), plasminogen activator inhibitor 1 (PAI-1), and thrombomodulin were also measured. The mean level of TAT on the day when OD occurred was significantly higher compared with the maximum level of TAT in septic patients without OD (P < .01) or postoperative patients (P < .01). There was no difference in PIC levels between the three groups. The TAT/PIC ratio was significantly higher in septic patients with OD compared with the other groups (P < .001). Septic patients with OD showed higher levels of PAI-1 (P < .001) but not of t-PA. Thrombomodulin levels were significantly higher in the septic patients with OD compared with the others (P < .001). We conclude that suppression of the fibrinolytic system contributes to the imbalance between coagulation and fibrinolysis, and that this hypercoagulable millieu on the endothelial surface leads to the onset of OD.
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PMID:Alterations in coagulation and fibrinolysis during sepsis. 869 88

Cirrhosis is associated with compromised hemostasis and coagulopathy during orthotopic liver transplantation (OLT). It has been suggested that hemostasis is better preserved during OLT in primary biliary cirrhosis (PBC) than other cirrhotic states. The aim of this study was to compare coagulation and fibrinolysis in 15 patients with PBC with 31 patients with other liver disease before and during OLT. Preoperatively, both groups had subnormal mean levels of prekallikrein, factor XIIa, antithrombin III (ATIII), plasminogen, and alpha2-antiplasmin. C1 esterase inhibitor and kallikrein inhibition in PBC was higher than the normal range (P < .01), but not in non-PBC. Non-PBC had lower median fibrinogen levels and shorter euglobulin clot lysis times (ECLT) (P < .05). Tissue plasminogen activator (tPA) antigen levels did not differ between groups but were elevated from the normal range, as were median thrombin-antithrombin complexes (TAT). Plasminogen activator inhibitor (PAI) activity was significantly higher in PBC (0.0041). Perioperatively in the PBC group during the early anhepatic phase of OLT, there was more thrombin generation, as evidenced by higher TAT levels (P = .0455) and less hyperfibrinolysis with longer ECLTs. We hypothesize that there is a preserved capacity to generate thrombin and less fibrinolytic activation during the anhepatic phase of OLT, and we suggest that, in PBC, the use of antifibrinolytic agents may have an adverse effect.
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PMID:Coagulation and fibrinolysis in primary biliary cirrhosis compared with other liver disease and during orthotopic liver transplantation. 904 19

Hemodynamic forces modulate various endothelial cell functions even in the presence of cytokines under gene regulation. We have investigated the effect of shear stress on the coagulation and fibrinolysis systems in cultured human umbilical vein endothelial cells (HUVECs) perturbed by cytokines, using modified cone-plate viscometer. Thrombomodulin (TM), a surface glycoprotein receptor for thrombin that catalyzes the activation of the protein C anticoagulant pathway, and tissue factor (TF), a transmembrane glycoprotein that plays a central role in blood coagulation, are important regulators for coagulation in endothelium. Shear stress of 18 dynes/cm2 increased the expression of TM either in the presence or absence of TNF alpha (100 U/ml). In contrast, shear stresses of 6 approximately 24 dynes/cm2 decreased the expression of TNF alpha-induced TF in a shear intensity- and exposure time- dependent manner Tissue plasminogen activator(t-PA), which converts plasminogen to plasmin to degrade fibrin clot, and plasminogen activator inhibitor-1 (PAI-1), which inhibits t-PA function, play central roles in fibrinolysis in the endothelium. Treatment of the cells with IL-1 beta or TNF-alpha under static conditions had no effect on t-PA secretion, while release of PAI-1 increased. When cells were exposed to increasing shear stress up to 24 dynes/cm2, levels of t-PA significantly increased relative to shear stress, while PAI-1 secretion decreased gradually. In the presence of IL-1 beta or TNF-alpha, the increased production of t-PA was further augmented. These results clearly indicate that shear forces act as an important regulators of the coagulation and fibrinolysis systems in endothelium, to maintain antithrombogenicity of blood vessels.
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PMID:[Regulation of antithrombogenicity in endothelium by hemodynamic forces]. 913 94

Hepatic veno-occlusive disease (VOD) is a major complication after bone marrow transplantation (BMT). Its prediction, diagnosis and treatment remain unclear. Examination was made of changes in hemostatic parameters in patients with or without VOD after BMT. Twenty-seven children were studied following BMT. Eight of them developed VOD. Tissue plasminogen activator (t-PA), plasminogen activator inhibitor 1 (PAI-1), thrombomodulin (TM), von Willebrand factor (vWF), factor VII, fibrinogen (FBG), FDP, D-dimer (D-D), plasminogen (PLG), thrombin-antithrombin III (TAT), alpha 2-plasmin inhibitor/plasmin complex (PIC), antithrombin III (AT-III), protein C, N-terminal propeptide for type III procollagen (P-III-P), were measured weekly from pre-BMT to day 28 after BMT. In VOD patients, t-PA and PAI-1 significantly increased (P < 0.05) and FBG significantly fell during the post-transplant period (P < 0.05). Significantly low AT-III and PLG were also noted before VOD (P < 0.05). There were no changes in other hemostatic parameters. t-PA, PAI-1 and FBG would thus appear useful markers for the diagnosis of VOD, and AT-III and PLG, predictive markers for VOD. The coagulation-fibrinolysis system following endothelial cell damage may contribute to the onset of VOD.
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PMID:Changes in hemostatic parameters in hepatic veno-occlusive disease following bone marrow transplantation. 915 66


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